1. Field of the Invention
The present invention relates to a catalyst for use in the polymerization and copolymerization of alpha-olefins such as ethylene and to the process of polymerizing alpha-olefins using the catalyst.
2. Related Art
Highly active polymerization catalysts have been described in the literature which are formed by milling or pulverizing MgCl.sub.2 in the presence of an electron donor such as ethyl benzoate followed by treatment with a transition metal compound such as TiCl.sub.4. The function of the ethylbenzoate is generally accepted to be the stabilization of small crystallites of MgCl.sub.2 to form a more active catalyst surface.
The present invention is directed toward a substitute for ethylbenzoate in the form of an inorganic halide, namely scandium halide, which has the same crystal structure as MgCl.sub.2. Unlike ethyl benzoate, the ScCl.sub.3 for example becomes an integral part of the support lattice and is not effectively extracted by the aluminum alkyl cocatalyst. Since the concentration of the cocatalyst is not reduced by side reactions with an electron donor of the type normally used, a highly active catalyst results when the ScCl.sub.3 doped support is treated with titanium and/or vanadium compound.
U.S. Pat. No. 4,143,223 discloses the preparations of Ti containing catalyst by mechanically pulverizing a magnesium compound and organic ester and impregnating the resultant solid with TiCl.sub.4 which was then used with an alkyl aluminum cocatalyst to polymerize an alpha-olefin.
U.S. Pat. No. 2,907,757 discloses that scandium halide combined with a Grignard reagent in an inert hydrocarbon solvent is polymerization catalyst for ethylene.
U.S. Pat. No. 4,384,982 discloses reacting scandium halide with a transition metal compound and an organometallic compound to produce a solid which is treated with a halide ion exchange source to produce an olefin polymerization catalyst. Mixing the catalyst with magnesium chloride was observed to enhance catalyst productivity in polymerization of alpha-oleins.
It is an advantage of the present invention that mechanically pulverized magnesium and titanium and/or vanadium catalysts having improved polymer productivity are produced.